Any project should have marked targets that must be planned and divided into several tasks and, during development, do tracking to meet the deviations that occur and take appropriate decisions to have it under control.

To successfully complete a project have to meet its initial objectives (not to mention the changes that arise during the phases of the project due to changes by customers, test users, development team, project managers, potential market, etc..) and one of the main objectives is to meet the originally scheduled completion date, usually imposed by customers.

A good help is to represent the project tasks so that can change the scenarios at any time knowing what is been done and what remains to be done to allocate more or less time before there is risk to meet the objectives.

If you don't have MS Project you can use MS Excel to build a Gantt Chart with many of its features if you read this topic and begin this September with good intentions and projects.

Gantt Chart with 3 scenarios: Optimistic, Realistic and Pessimistic

The Gantt Charts usually don't consider anything more than a scenario but this provides 3 scenarios or possible cases:

Optimistic (best case): with optimal time of shorter duration historic of tasks.

Realistic (scheduled case): with the modal duration time of greater historical frequency of tasks.

Pessimistic (worst case): with the worst time, that is the longest historical duration of tasks.

Besides, of course, being able to change the names of tasks, cells that can be modified are marked with yellow background color:
C4 - Percent for the optimistic scenario.
C5 - Percentage for the realistic scenario.
C6 - Percent for the pessimistic scenario.
O9 - Scheduled starting date of the project.
F9 a F20 - Initial duration of each task scheduled on weekdays.
W9 a W20 - Actual dates of completion of tasks.
X9 a X20 - Days to be added at the end of a task to start the next task.
D10 a D20 - Predecessor tasks of each task, separated by commas.

The different scenarios of the Gantt Chart are selected through dropdown list in the next cells:
O2 - Gantt o Scenarios of the Gantt Chart.
O7 - Optimistic, Realistic and Pessimistic with the 3 possible scenarios.